(1) Field of the Invention
The invention relates to a device for electron-beam lithography for manufacturing a master disk, comprising means for moving the master disk, means for generating a row of electron beams and means for directing electrons from said row of beams onto a track on the master disk.
(2) Description of Related Art
The invention also relates to a method for the electron-beam lithography manufacture of a master disk, wherein a row of electron beams is generated and directed onto a track on the master disk.
Such a device and method are known from U.S. Pat. No. 5,216,219.
According to said US patent, information is written onto a so-called master disk by means of one or more controllable electron beams.
Electron-beam lithography has developed after the limit was reached in optical lithography as regards the smallest spot that could reasonably be formed by optical means. This complicates the step of moving on to next generations of high-density formats that can be recorded on an optical plate. Electron-beam lithography makes it possible to record significantly smaller pits/grooves on an optical plate. Recording on an optical plate takes place both by making a copy of a so-called master disk formed of a hard material and by writing user information onto optical disks.
Electrons are electrically charged particles which are all identically charged, so that electric repulsion occurs among them. The more electrons are contained within a particular volume, the stronger the mutual repulsion. The consequence of this is that the smaller the spot that is intended to be made of an electron beam, the smaller the beam intensity should be in order to prevent the electron density becoming so large that noticeable repulsion starts to take place among the electrons. One consequence of this is that the recording time for making a master disk will be very long. It has been attempted to find a solution by using a more sensitive resist, to be sure, but this offers only a limited solution, since the signal will exhibit noise when the number of electrons is too low.
The object of the invention is to provide a system by which various combinations of pits and grooves can be written within a short time and in a flexible manner, and wherein the above-described drawbacks are largely or completely eliminated.
In order to accomplish that objective, a device for electron-beam lithography apparatus according to the invention is characterized in that the row of beams extends substantially parallel to the track, in that an aperture element comprising at least one aperture is provided, in that first lens means are disposed between the means for generating said row of beams and the aperture element for the purpose of deflecting electrons in said row of beams in the direction of said at least one aperture, and in that second lens means are disposed between the aperture element and the master disk for the purpose of deflecting electrons that have passed through said at least-one aperture in an intended direction onto the master disk, and in that controllable means for deflecting electrons in said row of beams to a position substantially beside the aperture are disposed between the means for generating said row of beams and said aperture element.
A method according to the invention is characterized in that said row of electron beams is applied in a direction substantially parallel to the track on the master disk, in that said row of beams is deflected through an aperture in an aperture element by a first lens element and projected onto the master disk by a second lens element, and in that said beams are controlled either to be directed at the aperture or not to be directed at the aperture.
As a result of the above aspects, one and the same spot on the master disk can be xe2x80x9cexposedxe2x80x9d to an electron beam from the row of beams a number of times, wherein successive electron beams from said row of beams are used for successive exposures. The controllable means make it possible either to direct a beam from said row of beams through the aperture, similarly to the process of xe2x80x9cexposingxe2x80x9d the resist on the master disk, or not to direct said beam through the aperture, similarly to the process of xe2x80x9cnot exposingxe2x80x9d the resist on the master disk. In this manner it is ensured that a very short xe2x80x9cexposure timexe2x80x9d is used for each exposure of the resist to a beam of electrons, whilst a sufficiently long overall xe2x80x9cexposure timexe2x80x9d, in particular sufficiently long for minimizing the amount of noise in the signal, can be achieved by selecting a sufficiently large number of beams in the row of beams.
From U.S. Pat. No. 5,561,008 there is known an electronic lithography apparatus wherein an electron beam is transmitted through a mask, and wherein the scattered and unscattered electrons of the beams that are transmitted through the mask are projected onto an aperture element comprising at least one aperture via a first lens, and wherein subsequently said electrons are projected onto the disk material coated with a layer of an electron-sensitive material by a second lens disposed between the aperture element and the master disk. In this case the repeated projection of a complete two-dimensional pattern via electron optics and an aperture onto an electron-sensitive resist on a disk of semiconductor material is concerned. The technology disclosed in said patent is not directed at the writing of pits/grooves in a rotating master disk, nor does it refer thereto.
One preferred embodiment of a device for electron-beam lithography according to the invention is characterized in that control means are present for operating the controllable means in succession, each time from a first beam from said row of beams until a last beam from said row of beams, by means of a signal train, which is based on one and the same, respectively time-shifted signal train for each beam from said row of beams.
One preferred embodiment of a method according to the invention is characterized in that, seen in the direction of movement of the track relative to the row of beams, all controlled beams are controlled in succession, from a first beam from the row of beams to a last beam from said row of beams, by a signal train, which is based on one and the same, respectively time-shifted, signal train for each beam from said row of beams.
In this manner it is achieved that the quality of the signal that is eventually written onto the master disk, using a very low intensity per electron beam, is similar to that of the signal that is written by means of a beam having a much higher intensity. The dimensions of the pits/grooves, however, match the low intensity of the individual electron beams from the row of beams that are projected onto the master disk via the aperture by the first and the second lens means.
One preferred embodiment of the invention is characterized in that controllable deflection means are provided for deflecting one or more beams from the row of beams in a direction substantially perpendicularly to a direction of movement of the track.
As a result of this arrangement, also so-called xe2x80x9ctwo-spotxe2x80x9d applications are possible. With such applications, two tracks are written closely together at the same time. Another result is that it is possible to write a so-called xe2x80x9cwobblexe2x80x9d track, or even two xe2x80x9cwobblexe2x80x9d tracks beside each other.
Yet another embodiment of a device for electron-beam lithography according to the invention is characterized in that said controllable means cause magnetic deflection.
A suitably selected magnetic deflection, for example by means of one or more coils that generate a magnetic field comprising a component which is not axial with the respective beam from the row of beams, makes it possible to ensure that the respective electron beam is strongly scattered in many directions. The advantage of this is that the beam is not projected in concentrated form at one specific spot on the aperture element, but that it is distributed over said element. This is advantageous in connection with the thermal load on the aperture element.